Further imir disambiguation for avifdec --info

apps/shared/avifutil.c

diff --git a/apps/shared/avifutil.c b/apps/shared/avifutil.c
index db5f813..99cfa6c 100644
--- a/apps/shared/avifutil.c
+++ b/apps/shared/avifutil.c
@@ -46,7 +46,9 @@
             printf("    * irot (Rotation)      : %u\n", avif->irot.angle);
         }
         if (avif->transformFlags & AVIF_TRANSFORM_IMIR) {
-            printf("    * imir (Mirror)        : %u (%s)\n", avif->imir.axis, (avif->imir.axis == 0) ? "Vertical" : "Horizontal");
+            printf("    * imir (Mirror)        : %u (%s)\n",
+                   avif->imir.axis,
+                   (avif->imir.axis == 0) ? "Vertical axis (\"left-to-right\")" : "Horizontal axis (\"top-to-bottom\")");
         }
     }
 }